New Nanosensor Sniffs Bombs, One Molecule At A Time

Imagine a piece of metal 30,000 times thinner than one of the hairs on your head. Mixed with a little protein from bee venom, that microscopic filament becomes the most powerful explosives-detection system in history, able to detect a single molecule of dangerous chemicals.

Now imagine having that in an airport. No need for taking a pornographic photograph or having your genitals massaged by the Transportation Security Agency. And a nanotechnology specialist may have hastened that happy day for homeland security.

Michael Strano, an associate professor of chemical engineering at the Massachusetts Institute of Technology, spent the past two years testing out the boundaries of nanotech in explosives detection. For less than $US200,000, he took it practically to the atomic limit. "There's no further improvement in the sensor part you can get," Strano tells Danger Room. "It's the last word in sensors."

Some of his colleagues aren't quite so sure. Strano's system is promising, they say. But they have questions about bringing Strano's sensor into the field.

The science behind the Strano's sensor is complex. But here's the simplest way of breaking it down. Put bee venom on a carbon rod and you've got yourself a sensor.

Believe it or not, bees are powerful bomb sleuths. That's why Darpa wanted to enlist them to find explosives, landmines and "odors of interest" in the early 2000s. As it turns out, inside of every bee sting is a small fragment of a protein called a peptide that has an uncanny property.

"When it wraps around a small wire, that allows it to recognise ‘nitro-aromatics'," Strano explains, the chemical class of explosives like TNT. That wire is a carbon nanotube, a mere one atom thick.

Put that against a nitro-aromatic treated with the bee peptide, and take a look through a near-infrared microscope. "The light from the carbon nanotube will fluoresce - so red that your eye can't see it," Strano says. "What you'd see in the microscope is: The nanotube would flicker off and on." A single molecule of the explosive material would set off the sensor.

The ion-mobility spectrometers currently used to spot bombs in US airports are "poor machines," says Ray von Wandruszka, chairman of the chemistry department at the University of Idaho, who's worked on atmospheric explosive detection since 1989. The spectrometers typically detect chemicals in the "low parts per billion" range. Strano's sensor would be vastly more sensitive.

If it works, that is.

Neither von Wandruszka nor his colleague at the university, Patrick Jerzy Hrdlicka, have read Strano's paper. But Hrdlicka is intrigued.

"Single-molecule detection is clearly interesting and something people are striving for these days," Hrdlicka says. "Surely that's going to be a very interesting result, provided their sensor technology is reproducible, easy to commercialise, easy to use, and so on."

Indeed, if so, there's a market for it that extends far beyond the airports. The threat from homemade bombs to troops at war has prompted billions in spending over the last decade.

But the state of the art technology is still a dog's nose, according to the Pentagon's anti-bomb squad - which is why the Navy SEALs took a canine companion along when raiding Osama bin Laden's house.

Nanoscience isn't even the most baroque method of explosives detection around. A biologist at Colorado State University is breeding plants that change color in the presence of bomb materials.

There are limits, though. Von Wandruszka thinks a sensor that sniffs down to a single molecule would be subject to false positives. And while the sensor doesn't have a "clear distance after which it can't be used," Strano says, it's meant more for "looking for contaminated surfaces" - not remote detection.

At the same time, while Strano's sensor isn't designed for detecting explosive compounds at a distance, there's a simple engineering solution: make the device mobile.

It's an engineering and finance problem to get the sensor mobile, Strano figures, a matter of shrinking down an infrared microscope that can see the sensor's flickering signal. Because his work has been funded by the Army's Institute for Soldier Nanotechnologies at MIT, he might be able to find some deep-pocket sponsors who'd be interested in taking it mobile.

"If you walked through the airport after a shower, you'd be dripping wet," he explains. "Anyone you touch or brushed up against would get a little bit wet. That can help me follow everyone you've touched. But if I get closer to where you are, I'll find a lot of wetness." Beats having your junk touched.

Photo: Los Alamos National Laboratory

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